The present invention relates to the field of machine recognition of magnetically imprinted characters on a document and more particularly to a method and apparatus for identifying an input waveform representing an unknown character.
In single-gap magnetic character reading systems, a single analog input waveform is obtained by passing the characters to be sensed, normally printed on a document, beneath a magnetic read head at least as wide as the height of the characters and having a single flux gap. The signal generated by the read head is a derivative waveform representing the rate of change of magnetic flux transversing the head as the characters are scanned. Since the distribution of ink, and thus flux, associated with each different character is unique, the waveform derived for each different character uniquely identifies that character.
To simplify the timing of the waveform analysis process, the characters are provided with stylized geometric features which impart anticipatable timing characteristics to the derived waveforms. Thus, in accordance with this means for reader identification, each character of the E-13B font, for example, is divided into a predetermined number of vertical segments corresponding to a location of bar portions of the character. The E-13B characters are designed such that the distribution of ink undergoes significant change only at the boundaries between each segment. Hence, peak fluctuations in the derived waveform caused by these variations in ink distribution can occur at only predetermined times during the character scanned.
Prior character recognition systems have incorporated circuits for determining the amplitude of each of the peaks of the waveform which uniquely represent the unknown character. These peak amplitudes and their positions are normalized and then correlated with the known peak characteristics of each of the E-13B characters to identify the character read. An example of this type of recognition system may be found in the U.S. Pat. No. 4,143,356 and assigned to the present assignee. Ideally, a recognition system should be able to correctly classify an input waveform as being the character it represents regardless of waveform distortions produced by printing apparitions. In actual practice, it has been found that the characters imprinted on a document may be distorted such that portions of the symbol of the character within the symbol outline are not covered with magnetic ink. Such a distortion may occur due to imperfections of the printing device employed to imprint a character on a document. Also, the pigment of the magnetic ink used by the printing device may not have been uniformly dispersed throughout the character outline. Such poorly defined or misprinted characters produce voltage waveforms that may resemble the waveform of a character other than the character that was intended to be printed, thereby causing a misread. It has also been found that documents become splattered with ink particles during the printing process, which particles cause corresponding spurious signals in the read head. All of these situations have caused misread operations in those recognition systems which are based solely on the correlation of peak amplitudes with a character reference standard. It is therefore an object of this invention to provide a magnetic character recognition system which overcomes the above-mentioned problems found in the prior art. It is a further object of this invention to provide a character recognition system which will correlate features of an unknown character with known characters at a relatively high rate of speed. It is a further object of this invention to provide a character recognition system which measures the "degree of risk" associated with classifying a waveform as a certain character.